I've tried this before, and without good results. The best results were either a diminishing of the vocals, or distortion of the rest of the music so bad it didn't MATTER the vocals were gone.
Most karaoke software simply takes out the "center" channel on music, leaving everything else behind. Since vocals are normally a mono signal panned to the center, it would theoretically be simple to remove. In practice, nothing does a good job of it. Even ones with adaptive algorithms to intelligently seperate voice from instrument fail misserabbly.
JigPu